Vacuum tube circuit to approximate an ideal switch over a broad temperature range



2 4 1 May 1967 v R. w. ECKSTElN, JR 9 VACUUM TUBE CIRCUIT TO APROXIMATE AN IDEAL SWITCH OVER A BROAD TEMPERATURE RANGE Filed Nov. 2', 1964 United States Patent 3,320,491 VACUUM TUBE CIRCUIT T0 APPROXHMATE AN IDEAL SWITCH-I OVER A BROAD TEMPERATURE RANGE Royal W. Eclrstein, In, Indianapolis, Ind., assignor to the United States of America as represented by the Secretary of the Navy Filed Nov. 2, 1964, Ser. No. 408,440 Claims. (Cl. 317-142) ABSTRACT OF THE DISCLOSURE A relay switch control circuit having an electron flow control means in circuit with the electromagnetic actuator of the relay switch, one pair of the relay switch contacts placing an increased voltage on the control electrode of the electron flow control means during relay actuation to maintain the relay actuated (to avoid relay dropout due to the temperature change to change the resistance of the electromagnetic actuator) over a wide temperature range.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Background of the invention The present invention relates to circuitry for controlling the operation of a relay, and more particularly to a vacuum tube circuit for reliably controlling the operation of a relay over a temperature range in excess of 250 degrees centigrade (C.).

The prior art contains many circuits for controlling the opening and closing, or switching, of electrical relays in response to various control signals. However, most of these control circuits become ineffective or unreliable when the circuitry is required to function over a broad range of ambient temperatures. One of the causes of this unreliability with changing temperature is that the temperature coefficient of resistivity (i.e., the ratio of the change in resistivity due to a change in temperature of 1 degree centigrade relative to the resistivity at degrees Centigrade) of copper, which usually comprises a relay coil, is such that a large change in ambient temperature will produce a relatively large change in the resistance of the relay coil, thereby upsetting the circuit and preventing the relay from being reliably opened and/or closed by the control circuit.

Summary of the invention Various military and commercial applications of electronic and electromechanical equipment require the reliable operation of relay control circuitry over very broad temperature ranges. The present invention overcomes the disadvantage of prior art relay control circuitry and provides this required reliable relay control over a temperature range in excess of 250 degrees C. A novel arrangement of resistances and Zener diode circuitry in conjunction with a vacuum tube enable the invention to provide reliable relay control over a temperature range from below -65 degrees C. to above +200 degrees C. despite a considerable change in the effective resistance of the relay coil.

An object of the present invention is to provide reliable control of an electrical relay switching circuit over a broad range of ambient temperatures.

Another object is to provide circuitry for reliably closing, and opening after a predetermined time interval, an electrical relay in response to a trigger signal over a broad range of ambient temperatures.

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Brief description of the drawing Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment of the invention as schematically illustrated in the accompanying figure of drawing.

Description of the preferred embodiment Referring now to the figure of drawing, there is shown a specific embodiment of the invention in which an input terminal 11 for receiving a control, or trigger, signal is coupled via a conductor 12 to the grid electrode of a triode vacuum tube 13 which has its anode electrode coupled to one terminal of the control coil 14 of a multiple pole, double throw relay 15. The other terminal of coil 14 is coupled to a source of direct current potential 16. The cathode electrode of tube 13 is coupled via a resistance 17 and the parallel combination of a resistance 18 and a Zener diode 19 to ground potential. A resistance 21 is coupled between ground potential and conductor 12. A capacitance 22 is coupled between the junction of resistance 21 and conductor 12, and the movable contact arm 23 of the uppermost set of contacts of relay 15. When the core of relay 15 is not energized by coil 14, contact arm 23 is in such a position that capacitance 22 is coupled via a resistance 24 to ground potential, and when the core is energized, contact arm 23 causes capacitance 22 to be coupled to a source of direct current potential 25. Contact sets 26 and 27 are shown merely to represent that relay 15 includes several sets of contacts which are electrically independent of the invention, but which are mechanically Tube 13 7296 Relay 15 GE 3S2791FB100D9 Zener diode 19 volts 5 Capacitance 22 microfarads 4 Resistance 17 ohrns 390 Resistance 18 do 5,000 Resistance 21 do 100,000 Resistance 24 do 10,000 Input trigger pulse amplitude volts +28 DC. potential source 16 do +200 DC. potential source 25 do +28 It is to be understood that these particular components, values, and potentials are presented only for illustrative purposes and are not intended to limit the scope of the invention in any way.

Operation The operation of the invention occurs in the following manner. In the quiescent condition tube 13 will be conducting at a low level and there will be insufficient current flow through coil 14 to cause relay 15 to pull in or move from its quiescent position. This low level of current flow will be referred to as the relay off current. Thus contact arm 23 will remain in the position shown in the figure of drawing, thereby coupling capacitance 22 via resistance 24 to ground potential. During this quiescent period the reverse potential across Zener diode 19 is low and its reverse breakdown potential is not reached; therefore, diode 19 appears as a very high impedance to the fiow of low level oif current causing this current to flow through parallel resistance 18 to ground potential. Thus it can be seen that the level of off current may be adjusted to a desired level by selection of a particular value of resistance for resistance 18, or by utilizing an adjustable resistance for resistance 18. The invention will remain in this quiescent state throughout a wide range of ambient temperatures because resistance 18 may be made s-ufiiciently large to maintain the off current at a level considerably below that which is necessary to cause coil 14 to pull in relay 15, even though the resistance of coil 14 decreases with decreasing temperature.

Upon application of a positive trigger pulse to input terminal 11, conductor 12 will couple this pulse to the grid electrode of tube 13 causing it to conduct heavily, thereby raising the potential at the cathode of tube 13 and thus at the junction point of resistances 17 and 18, and Zener diode 19. The positive potential rise at this junction will be sufficient to cause Zener diode 19 to become reverse biased beyond its critical or breakdown value. Diode 1 9 will then be operating in its Zener control region and current conduction across the diode junction will increase rapidly while the voltage drop across the junction will remain essentially constant. This greatly increased current fiow from source 16 through coil 14, tube 13, resistance 17 and Zener diode 19 to ground potential causes relay 15 to pull in and will be referred to as the relay on current level. This on current level is determined by the amplitude of the positive pulse applied to input terminal 11, the characteristics of the particular Zener diode chosen for diode 19, and the value of resistance 17. As soon as this on current begins to flow, relay 15 is pulled in causing all movable contact arms of the various contact pairs therein to move to their other respective contact positions, thereby performing the first phase of the desired switching function for the electrically independent pairs of contacts such as those represented by pairs 26 and 27 in the figure of drawing. Thus it can be seen that the application of a positive trigger pulse of short duration will momentarily cause the invention to switch from the ofi current level, or its quiescent state, to the on current level pulling in relay 15. The invention must also return to the off current level after a predetermined time interval to cause relay 15 to drop out and return electrically independent contact pairs 26 and 27 to their respective quiescent positions in order to complete the last phase of the desired switching function. This occurs in the following manner. As soon as the trigger pulse applied to input terminal 11 causes relay 15 to be momentarily pulled in, movable contact arm 23 moves to its upper position in the figure of drawing coupling the grid electrode of tube 13 via conductor 12 and capacitance 22 to positive potential source 25, whose magnitude is chosen to approximately equal the amplitude of the positive pulse applied to input terminal 11. Capacitance 22 is charged to the level of source 25, and this potential applied to the grid electrode of tube 13 maintains that tube in a heavily conducting state thereby holding relay 15 pulled in until capacitance 22 discharges, through resistance 21 in parallel with the series combination of resistance 17 and diode 19, to a level at which the conduction through tube 13 decreases sufiiciently to cause the potential across Zener diode 19 to no longer exceed its reverse breakdown voltage. At this point, diode 19 becomes a very high impedance to this fiow of current in its reverse direction causing the current flow to pass through resistance 18 thereby lowering it from the on level to the oif level and causing relay 15 to drop out or return to its quiescent position, completing the last phase of the desired switching function. The predetermined amount of time relay 15 remains on or pulled in, fter being placed in that state initially by the invention in response to the trigger pulse applied to input terminal 11, is determined in large part by capacitance 22 and resistance 21; therefore, the values of these components should be selected so as to provide the desired on time.

The invention enables reliable control of the oif and on functioning of relay over a very broad temperature range despite a large change in the effective resistance of relay coil 14 because the level of the ofif current may be controlled by the selection of resistance 18 and made sufliciently low so that the large decrease in the resistance of coil 14 caused by operation of the circuit in a very low ambient temperature does not permit this otf current level to increase sufiiciently to pull in the relay in the absence of a trigger signal, which would occur with many circuits of the prior art. Also, the level of the on current may be controlled by the selection of resistance 17 and Zener diode 19, and made sufficiently high so that the large increase in the resistance of coil 14 due to operation of the circuit in a very high ambient temperature does not cause this on current level to drop sufficiently to result in relay 15 dropping out or being cut off, which would happen in many circuits of the prior art. It can be seen that the relay off current and on current levels of the present invention are determined principally by three independent circuit elements, resistance 18 and resistance 17 in series with Zener diode 19, respectively, thus no compromise in the choice of these two levels is necessary in the present invention. The ratio of relay on current to off current may be made as large as desired, limited only by the particular characteristics of tube 13 and Zener diode 19.

Thus it becomes apparent from the foregoing description and annexed drawing that the invention, a reliable, temperature-stable relay control circuit, is a useful and practical device having many applications in the fields of electronics and electromechanical control.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A reliable electronic switching circuit comprising:

an electron flow control means including an emitting electrode, a collecting electrode, and a control electrode, said control electrode being coupled to an input terminal means for receiving control signals;

an electromagnetic relay means having a control coil and a plurality of sets of contacts, each of said sets of contacts including first and second fixed contacts and a movable contact arm which in a quiescent position is in contact with said first fixed contact and when in an energized position is in contact with said second fixed contact, said control coil being coupled between said collecting electrode of said electron fiow control means and a source of direct current potential, one set of said plurality of sets of contacts having its said first fixed contact resistively coupled to ground potential and its said second fixed contact coupled to a source of direct current potential;

an electrical storage means having one terminal thereof coupled to said control electrode of said electron flow control means and further resistively coupled to ground potential, and the other terminal coupled to said movable contact arm of said one set of said plurality of sets of contacts of said relay means; first and second resistance means coupled in series between a source of ground potential and said emitting electrode of said electron fiow control means; and

a potential controlled, variable resistance means coupled in parallel with said second resistance means.

2. A reliable electronic switching circuit as set forth in I claim 1 wherein said electron flow control means comprises a triode vacuum tube, said emitting, collecting and control electrodes thereof being cathode, anode, and grid electrodes, respectively.

3. A reliable electronic switching circuit as set forth in claim 1 wherein said electrical storage means comprises a capacitance means of such capacity as necessary to provide, in association with resistance means, a time constant sufficient to cause said electronic switching circuit to maintain said electromagnetic relay means in an energized state for a predetermined period of time.

4. A reliable electronic switching circuit as set forth in claim 1 wherein said potential controlled, variable resistance means comprises a Zener diode.

5. A reliable electronic switching circuit as set forth in claim 2 wherein said electrical storage means comprises a capacitance means of such capacity as necessary to provide a time constant suflicient to cause said electronic switching circuit to maintain said electromagnetic relay means in an energized state for a predetermined period of time.

6. A reliable electronic switching circuit as set forth in claim 5 wherein said potential controlled, variable resistance means comprises a Zener diode.

7. An electronic circuit for reliably controlling the operation of an electromagnetic relay means throughout a broad range of ambient temperatures comprising:

an electron flow control means including an emitting electrode, a collecting electrode, and a control electrode, said control electrode being coupled to an input terminal means for receiving control signals;

an electromagnetic relay means having a control coil and a plurality of sets of contacts, each of said sets of contacts including first and second fixed contacts and a movable contact arm which, when in a quiescent position contacts said first fixed contact, and when in an energized position contacts said second fixed contact, said control coil being coupled between said collecting electrode of said electron flow control means and a source of direct current potential, one set of said plurality of sets of contacts having its said first fixed contact resistively coupled to ground potential and its said second fixed contact coupled to a source of direct current potential;

a capacitance means having one terminal thereof coupled to said control electrode of said electron flow control means and further resistively coupled to ground potential, and the other terminal coupled to said movable contact arm of said one set of said plurality of sets of contacts of said relay means;

first and second resistance means coupled in series between a source of ground potential and said emitting electrode of said electron flow control means; and

a potential controlled, variable resistance means coupled in parallel with said second resistance means.

8. An electronic circuit for reliably controlling the operation of an electromagnetic relay means throughout a broad range of ambient temperatures as set forth in claim 7 wherein said electron flow control means comprises a triode vacuum tube, said emitting, collecting, and control electrodes thereof being cathode, anode, and grid electrodes, respectively. 5 9. An electronic circuit for reliably controlling the operation of an electromagnetic relay means throughout a broad range of ambient temperatures as set forth in claim 8 wherein said potential controlled, variable resistance means comprises a Zener diode.

10. An electronic circuit for reliably controlling the operation of an electromagnetic relay means throughout a broad range of ambient temperature comprising:

a triode vacuum tube means including cathode, anode, and grid electrodes, said grid electrode being coupled to an input terminal means for receiving control signals;

an electromagnetic relay means having a control coil and a plurality of sets of contacts, each of said sets of contacts including first and second fixed contacts and a movable contact arm which, when in a quiescent position contacts said first fixed contact, and when in an energized position contacts said second fixed contact, said control coil being coupled between said anode electrode of said vacuum tube means and a source of direct current potential, one set of said plurality of sets of contacts having its said first fixed contact resistively coupled to ground potential and its said second fixed contact coupled to a source of direct current potential;

a capacitance means having one terminal thereof coupled to said grid electrode of said triode vacuum tube means and further resistively coupled to ground potential, and the other terminal coupled to said movable contact arm of said one set of said plurality of sets of contacts of said relay means;

first and second resistance means coupled in series between a source of ground potential and said cathode electrode of said triode vacuum tube means; and

a voltage controlled, variable resistance means coupled in parallel with said second resistance means.

References Cited by the Examiner UNITED STATES PATENTS 8/1963 Hickey et al. 328--67 References Cited by the Applicant UNITED STATES PATENTS 8/1960 Beck. 11/ 1962 Cody.

3/1963 White. 11/ 1963 Pederson. 6/1964 Freeborn.

OTHER REFERENCES Tele-Tech and Electronic Industries, October 1953, page 94.

MILTON o. HIRSHFIELD, Primary Examiner.

J. A. SILVERMAN, Assistant Examiner. 

1. A RELIABLE ELECTRONIC SWITCHING CIRCUIT COMPRISING: AN ELECTRON FLOW CONTROL MEANS INCLUDING AN EMITTING ELECTRODE, A COLLECTING ELECTRODE, AND A CONTROL ELECTRODE, SAID CONTROL ELECTRODE BEING COUPLED TO AN INPUT TERMINAL MEANS FOR RECEIVING CONTROL SIGNALS; AN ELECTROMAGNETIC RELAY MEANS HAVING A CONTROL COIL AND A PLURALITY OF SETS OF CONTACTS, EACH OF SAID SETSD OF CONTACTS INCLUDING FIRST AND SECOND FIXED CONTACTS AND A MOVABLE CONTACT ARM WHICH IN A QUISCENT POSITION IS IN CONTACT WITH SAID FIRST FIXED CONTACT AND WHEN IN AN ENERGIZED POSITION IS IN CONTACT WITH SAID SECOND FIXED CONTACT, SAID CONTROL COIL BEING COUPLED BETWEEN SAID COLLECTING ELECTRODE OF SAID ELECTRON FLOW CONTROL MEANS AND A SOURCE OF DIRECT CURRENT POTENTIAL, ONE SET OF SAID PLURALITY OF SETS OF CONTACTS HAVING ITS SAID FIRST FIXED CONTACT RESISTIVELY COUPLED TO GROUND POTENTIAL AND ITS SAID SECOND FIXED CONTACT COUPLED TO A SOURCE OF DIRECT CURRENT POTENTIAL; AN ELECTRICAL STORAGE MEANS HAVING ONE TERMINAL THEREOF COUPLED TO SAID CONTROL ELECTRODE OF SAID ELECTRON FLOW CONTROL MEANS AND FURTHER RESISTIVELY COUPLED TO GROUND POTENTIAL, AND THE OTHER TERMINAL COUPLED TO SAID MOVABLE CONTACT ARM OF SAID ONE SET OF SAID PLURALITY OF SETS OF CONTACTS OF SAID RELAY MEANS; FIRST AND SECOND RESISTANCE MEANS COUPLED IN SERIES BETWEEN A SOURCE OF GROUND POTENTIAL AND SAID EMITTING ELECTRODE OF SAID ELECTRON FLOW CONTROL MEANS; AND A POTENTIAL CONTROLLED, VARIABLE RESISTANCE MEANS COUPLED IN PARALLEL WITH SAID SECOND RESISTANCE MEANS. 